1. Field of the Invention
The present invention relates to an apparatus for positioning railroad tie plates along a railroad track and more specifically to a sensor assembly used with the apparatus for positioning the railroad tie plates along the railroad track.
2. Description of the Related Art
Railroad tracks generally consist of two parallel steel rails, which are laid on railroad ties. Railroad ties are normally laid on a bed of coarse stone known as ballast, which combines resilience, some amount of flexibility, and good drainage characteristics. Railroad ties spread the load from the rails over the ground and also serve to hold the rails a fixed distance apart. The railroad ties are generally spaced apart a distance of about twenty-two inches on center although the distance may vary. On an upper surface of the railroad tie, is a tie plate or base plate. The tie plate connects the rail and the tie. Fasteners, such as spikes, screws or the like are often driven through a hole in the tie plate to hold the rail. Alternatively the rails may be clipped to the tie plates.
The steel rails can carry heavier loads than any other material. The rails generally have a foot, a web extending upwardly from the foot and a head. Additionally, the rails are spaced apart a preselected distance corresponding to wheel spacing of trains. The preselected distance between rails is known in the art as the gauge distance.
Over time, deterioration and repeated loading stress requires that the railroad ties be replaced during maintenance. Machines which deliver and position railroad tie plates along a railroad track bed are known in the art. One such device taught in U.S. Pat. No. 6,807,909 comprises an apparatus having a tire that engages tie plates at an end of a feed conveyor. The tire is operated by a timing transmission arrangement in order to deposit a tie plate when the apparatus rolls a preselected distance. The apparatus delivers a tie plate at each railroad tie within the rail gauge or alternatively on a rail bed side, depending on the desire of the maintenance crew.
However, one problem with the use of timing arrangements to deposit railroad tie plates is that over longer distances and periods of time, the likelihood of mis-positioning railroad tie plates increases. This is due to mechanical tolerances which are magnified over periods of time and therefore require adjustment when such timing is off. Specifically, it would be desirable to affirmatively detect the location of an existing tie plate and cause the depositing of a replacement tie plate at that location along the railroad track.